1. (Field of the Invention)
The present invention generally relates to a television signal processing circuitry for use in a magnetic information recording and/or reproducing apparatus such as, for example, a video camera or the like and, more particularly, to a video signal processing system used in a converter for converting a line sequential signal into simultaneous signals for improving the signal-to-noise ratio (S/N ratio).
2. (Description of the Prior Art)
An example of the prior art video signal processing system disclosed in the Japanese Laid-open Patent Publication No. 62-122492, published June 3, 1987, is reproduced in FIG. 6 of the accompanying drawings. Referring to FIG. 6 for the discussion of the prior art, the video signal processing system comprises an adder 2 having one of two input terminals connected with a system input terminal 1, a first 1H delay circuit 3 for delaying an output from the adder 2 for a length of time equal to one horizontal period (1H period), and a second 1H delay circuit 4 for delaying an output from the first 1H delay circuit 3 for a length of time equal to 1H period and for supplying the 1H delayed output of the first 1H delay circuit 3 to the other of the input terminals of the adder 2.
The illustrated video signal processing system also comprises a first changeover switch 5 having a pair of fixed contacts 5a and 5b and a movable contact 5c, connected to a first output terminal 7, and a second changeover switch 6 having a pair of fixed contacts 6a and 6b and a movable contact 6c connected to a second output terminal 8. The fixed contacts 5a and 6b of the first and second changeover switches 5 and 6, respectively, are connected to an input terminal of the first 1H delay circuit 3, and the fixed contacts 5b and 6a of the first and second changeover switches 5 and 6, respectively, are connected to an output terminal of the first 1H delay circuit 3.
In practice, each of the changeover switches 5 and 6 used therein is employed in the form of an electronic switch capable of alternately assuming one of the two states in response to a switching signal applied thereto; one state being in position to connect the terminal 5a or 6a to the output terminal 7 or 8 and the other state being in position to connect the terminal 5b or 6b to the output terminal 7 or 8. However, each of the changeover switches 5 and 6 may be in the form of a electromechanical switch.
The prior art video signal processing system of the above described construction operates in the following manner which will be described with the aid of waveforms of signals appearing in various points in the circuitry of FIG. 6.
The line sequential signal inputted to the input terminal 1 is of a waveform shown by (a) in FIG. 7. This line sequential signal applied to the input terminal 1 includes R-Y and B-Y color difference signals appearing alternately at the input terminal 1 one for each 1H period. While the line sequential signal at the input terminal 1 is supplied to one of the two input terminals of the adder 2, the line sequential signal which has been passed through the first 1H delay circuit 3 and then through the second 1H delay circuit 4 and, hence, delayed a length of time equal to twice the 1H period, that is, 2H periods, is also supplied to the other of the two input terminals of the same adder 2. Because of the 2H period delay relative to the incoming line sequential signal, the R-Y and B-Y color difference signals do not mix up and the adder 2 alternately outputs the R-Y and B-y color difference signals.
A waveform shown by (b) in FIG. 7 represents that of a switching signal having logic high and low levels alternating with each other. For each 1H period, the movable contacts 5c and 6c of the first and second changeover switches 5 and 6 are selectively engaged to the fixed contacts 5a or 6a and 5b or 6b in synchronism with the logical high and low levels of the switching signal, respectively. Because of this, a synchronized R-Y color difference signal of a waveform shown by (c) in FIG. 7 and a synchronized B-Y color difference signal of a waveform shown by (d) in FIG. 7 can be obtained at the respective output terminals 7 and 8.
On the other hand, since the output signal from the second 1H delay circuit 4 is added by the adder 2 to the incoming line sequential signal, this feedback system constitutes a recursive comb-type filter for the purpose of improving the S/N ratio. The recursive comb-type filter is well known in the art and is disclosed in, for example, the Japanese Laid-open Patent Publication No. 55-150669, published Nov. 22, 1980, and U.S. Pat. No. 4,684,976 issued Aug. 4, 1987, both of which are herein incorporated by reference.
As hereinabove discussed, the prior art video signal processing system is so designed as to make use of the recursive comb-type filter for the purpose of improving the S/N ratio. However, it has been found having problems in that the sharpness of the amplitude-frequency characteristic of the filter cannot be changed and, therefore, the extent to which the S/N ratio of video signals can be improved cannot be variable.
Also, since interpolation of a signal when the line sequential signal is converted into simultaneous signals is carried out by the use of a signal appearing at the time preceding 1H period, it has been found that, in terms of a picture reproduced on a cathode ray tube, the contour of the reproduced picture tends to represent indents when a signal having no vertical correlation is inputted.
The Japanese Laid-open Patent Publication No. 62-58793, published Mar. 14, 1987, discloses an approach to improve the S/N ratio of video signals in the video signal processing circuitry. Even with this approach, not only can the S/N ratio be varied, but also the problem associated with the reproduced picture having the contour full of indents cannot be eliminated since no proper signal interpolation is employed.